Chair base



FIG. 1 is a perspective view of a chair base, showing my new design, the broken lines are for environmental purposes only and form no part of the claimed design;

FIG. 2 is a front elevational view thereof, the opposite end being a mirror image thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a rear elevational view thereof; and,

FIG. 6 is a bottom elevational view thereof. 

The ornamental design for a chair base design, as shown and described. 